Fluidized bed coating processes are well known and typically employ a fluidized bed dryer to coat discrete, finely-divided particles while the particles are suspended in an upwardly-moving gas stream in a coating chamber. While so suspended, a solution of the coating material is sprayed into the moving fluid bed of particles and the particles subsequently dryed and recovered, the recovered particles contain generally a thin coating of the coating material thereon. Fluidized bed dryers are commercially sold as standard pieces of engineering equipment and typical Wurster-type dryers and processes are described; for example, in U.S. Pat. Nos. 3,117,027, 3,196,827, 3,253,944, 2,648,609, 2,799,241, and 3,241,520. These patents disclose various fluidized bed dryers for the encapsulation of discrete particles with various coatings and various processes for coating such discrete particles in a fluidized bed technique.
One technique for the fluidized bed coating of discrete particles comprises suspending seed particles or crystals of about 20-200 mesh particles size or smaller of the particular material to be coated, such as a drug, in a fluidized bed chamber and, thereafter, contacting the suspended particles in the bed with an atomized mixture of a granulating material, so as to build up the seed particles to the desired size granules. The granulating materials are typically dispersed, dissolved or suspended in a volatile liquid such as water or an organic solvent and sprayed into the fluidized bed in a technique such as set forth in U.S. Pat. No. 3,089,824, issued May 14, 1963. Another technique of preparing agglomerate-type particles typically for subsequent use with tablets comprises employing a mixture of finely-divided powders in a fluidized bed and a solution of binder material is used to adhere the fine particles in the bed into larger particles, such as, for example, as described in U.S. Pat. No. 3,207,824, issued Sept. 21, 1965.
The coating of finely-divided particles in a fluidized bed provides for microencapsulation and may use a wide variety of discrete particles to be coated with a wide variety of materials to be deposited as a uniform coating layer on the particles. Encapsulating ingredients useful in fluidized bed coatings include but are not limited to: waxes; cellulose such as ethyl cellulose, hydroxy ethyl and propyl cellulose and methyl cellulose, and carboxymethyl cellulose; gelatins; gums; fatty acids like stearates; and natural and synthetic film-forming polymers such as shellac, starches, fluorocarbons, polyvinyl alcohol, polyvinyl acetate, vinyl chloride resins, acrylic resins, etc. The coating ingredients may be used as solvent or aqueous solutions, emulsions, dispersions, and melts. Materials capable of being employed in a fluidized bed include finely-divided solid material to be microencapsulated. Microencapsulation has been used for the encapsulation of pigments, in paint making, in paper making, in food products, pharamaceuticals, for beauty aids, laundry products, pressure-sensitive copying systems, paper coatings and a wide variety of other uses. In particular, it has been found that the microencapsulation technique is particularly useful for the encapsulation coating of materials, such as drugs, in order to provide a uniform coating and therefore provide for a delayed or controlled release of the active ingredient from the coated microcapsule. Microencapsulation techniques are set forth, for example, generally in Chemical Technology Review, No. 73, entitled "Microcapsulations and Microcapsulation Techniques" (1975), and Chemical Technology Review, No. 135, entitled "Microcapsules and other Capsules Advances Since 1975," both published by the Noyes Data Corporation.